The mammalian heart is essentially a pump that functions as a chemo-mechanical energy transducer. The chemical energy of metabolic substrates and oxygen is converted into the mechanical energy of blood pressure and flow by myocardial sarcomeres during cardiac contraction. The pump is periodic at a frequency of 1-2 Hz, with the contraction/ejection phase called systole and the relaxation/filling phase termed diastole.
The human heart is the center of the cardiovascular system, the system having two parallel circulations consisting of the pulmonary circulation and the systemic circulation. The pulmonary circulation receives blood from the venae cavae into the right atrium and right ventricle, and then pumps the cardiac output into the pulmonary arteries and through the lungs. The systemic circulation receives blood from the pulmonary veins, pumps the cardiac output through the left atrium and left ventricle to the aorta, systemic arteries, capillaries, and veins, and finally transmits blood back to the venae cavae. The mitral valve is positioned between the upper chamber, the left atrium, and the pumping chamber, the left ventricle. The left atrium acts in a capacitor function receiving blood from the lungs via the pulmonary veins throughout the cardiac cycle. The left ventricle fills during diastole by receiving blood from the left atrium as the mitral valve opens, and then during systole, the mitral valve closes and permits forward ejection of the blood from the left ventricle into the ascending aorta. The aortic valve is located between the left ventricle and aorta, and functions under normal conditions to allow unimpeded blood flow out of the ventricle and into the aorta during systole. During diastole, the aortic valve closes and prevents regurgitation backward into the left ventricle.
Surgical reconstruction of a patient's native valve is becoming standard for mitral valve disease. Whether considering mitral valve prolapse, pure annular dilatation, ischemic mitral regurgitation, or mitral endocarditis, repair is now routine, highly successful, and associated with low late failure rates. Even in rheumatic mitral disease, many surgeons are embarking on programs of aggressive repair, adding to ring annuloplasty the techniques of posterior leaflet augmentation with gluteraldehyde-fixed autologous pericardium, resection of the stenotic submitral apparatus with insertion of artificial GORTEX™ chords, leaflet decalcification, etc. The current goal is to achieve close to a 100% repair rate of mitral valve disorders and to markedly diminish prosthetic valve replacement. The advantages of repair versus replacement in this setting are well documented. The operative mortality rate (normalized for other factors) is lower, anticoagulation is not required in sinus rhythm, valve-related complications are less than with prosthetic valves, durability is excellent because the patient's own tissues do not degenerate, and late endocarditis is reduced because less foreign material is present. As such, these concepts for mitral valve disease are rapidly becoming standard-of-care in the field of cardiac surgery.
The aortic valve of a human heart can also become diseased, with aortic valve insufficiency occurring from a number of causes. A common cause is annular dilatation, with the sinuses of the Valsalva migrating outward and the inter-commissural distances expanding. Geometrically, this derangement not only increases the annular circumference, but also reduces the surface area of cusp coaptation. The coaptation angle of the cusps is changed essentially from being parallel and meeting at an acute angle to pointing at each other, wherein the cusps comprise a more obtuse arrangement. Eventually, a central gap of coaptation occurs and increasing aortic insufficiency begets more annular dilatation which begets more aortic insufficiency and the leak progressively increases.
Repair of a diseased aortic valve has not been met with the same success as experienced in reconstructing a diseased mitral valve. For about 10 to 15 years, the “commissural annuloplasty” technique has been used, but it can only be applied to mild-to-moderate secondary aortic insufficiency, usually in patients undergoing primary coronary bypass or mitral valve procedures. Commissural annuloplasty not only decreases annular circumference, but also tends to move the sinuses centrally, thus normalizing geometry and coaptation angles of the cusps. There is a limit, however, to the geometric abnormality that commissural annuloplasty can normalize, and because the entire annulus is not fixed by this procedure, the potential for further dilatation and recurrent aortic insufficiency exists.
As such, devices and methods have been proposed including, for example, U.S. Pat. No. 4,451,936 (“the '936 patent”), which teaches a supra-annular aortic valve. According to the '936 patent, the invention is applicable to mechanical heart valves and leaflet-type heart valves, and does not project into the aortic valve. In U.S. Pat. No. 5,258,021 (“the '021 patent”), an annuloplasty ring is described for insertion inside the aorta in the supra-annular region above the aortic valve annulus. The disclosed device appears circular from above and has three substantially sinusoidal shaped struts. In U.S. Patent Application Publication No. 2005/0228494 (“the '494 patent application”), a heart valve frame is described which can separate into a plurality of individual cusps after implantation. Additionally, the invention of the '494 patent application is preferably used with synthetic leaflets.
U.S. Pat. No. 6,231,602 (“the '602 patent”) describes an annuloplasty ring sutured to the tissue above the aortic valve annulus and also an infra-annular ring which can be sutured to the dense tissue immediately below the commissural-arterial wall intersection. Moreover, the infra-annular ring does not alter or even influence leaflet geometry in an organized manner, but instead constricts the infra-annular aorta to move the inferior aspects of the leaflets centrally rather than restore proper leaflet coaptation. Furthermore, as the ring of the '602 patent is apparently based on previous studies of the mitral valve, the '602 neglects the complexities of the 3-dimensional geometry of the aortic valve and ineffectively constricts either the supra-valvular or infra-valvular area. Also, the '602 patent describes the ring as only following the rough shape of the aortic tissue either above or below the valve annulus and neither provides an explanation of the proper sizing of the ring nor describes how the ring will be implanted within the patient.
The supra- or infra-annular rings and artificial valves of the prior art processes are generally circular (or axisymmetric) in shape. An axisymmetric shape is one that can be superimposed on itself more than twice in a 360 degree rotation. A circle and an equilateral triangle are examples of axisymmetric shapes. Unfortunately, such axisymmetric devices are generally not effective for the long term improvement of the aortic valve, and additionally, may require quite complicated surgical procedures.
What is desired, therefore, are improved devices for aortic valve repair or replacement. Also desired are processes for inserting and mounting such devices.